Transmission for vehicle

ABSTRACT

A transmission may include a first input shaft continuously receiving torque from a power source; a second input shaft selectively receiving torque from the power source through a clutch; a first countershaft and a second countershaft connected with the first input shaft and the second input shaft, respectively, by a transfer gear pair; coupling devices transmitting torque to the first countershaft and the second countershaft from the first input shaft and the second input shaft by selecting the transfer gear pairs; a one-way clutch disposed on the first countershaft to allow torque provided to the first input shaft to be transmitted only to the first countershaft from the first input shaft; and a shifting mechanism including a plurality of shift gear pairs having different gear ratios on the first countershaft, the second countershaft, and the output shaft.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2015-0094083, filed Jul. 1, 2015, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a transmission for a vehicle, and moreparticularly, to a transmission for a vehicle that reduces deteriorationof shifting ability, including a backward pulling effect.

Description of Related Art

An automated manual transmission can provide convenience for a driver,similar to an automatic transmission, by providing an automatic shiftingby means of an actuator while a vehicle is driven and can contribute toimproving fuel efficiency of a vehicle while maintaining powertransmission efficiency higher than an automatic transmission.

However, for an automated manual transmission based on a synchro-meshtype shifting mechanism, there is necessary a period where power from anengine is disconnected while automatic shifting is performed by anactuator that shifts gears, so torque is decreased and the shiftingability is deteriorated resulting in, for example, a backward pullingeffect of the vehicle when shifting.

In order to solve these problems, a technology of selectivelytransmitting power from an engine to an output shaft by selecting apower transmission path from the engine, depending on the driving statesof a vehicle, by providing a planetary gear set between the engine and asynchro-mesh type shifting mechanism has been proposed.

Further, a related art as another example, “Power train for a hybridelectric vehicle with automated manual transmission” has been proposed.

However, this technology requires two monitors to reduce deteriorationof shifting ability, so the manufacturing cost and weight of atransmission increase.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing atransmission for a vehicle that reduces deterioration of shiftingability, including a backward pulling effect when shifting.

In an aspect of the present invention, there is provided a transmissionfor a vehicle that includes: a first input shaft continuously receivingtorque from a power source; a second input shaft selectively receivingtorque from the power source through a clutch; a first countershaft anda second countershaft connected with the first input shaft and thesecond input shaft, respectively, by a transfer gear pair; couplingdevices transmitting torque to the first countershaft and the secondcountershaft from the first input shaft and the second input shaft byselecting the transfer gear pairs; a one-way clutch disposed on thefirst countershaft to allow torque provided to the first input shaft tobe transmitted only to the first countershaft from the first inputshaft; and a shifting mechanism including a plurality of shift gearpairs having different gear ratios on the first countershaft, the secondcountershaft, and the output shaft, and changing and outputting powerfrom the power source to the output shaft by selecting a shift gear paircorresponding to a speed of the vehicle, using a synchronizer.

The one-way clutch may be disposed in a power transmission path from anoutput transfer gear of the transfer gear pair on the firstcountershaft.

The one-way clutch may be disposed between the first countershaft andthe coupling device selectively coupling an output transfer gear of thetransfer gear pairs to the first countershaft.

The transfer gear pairs may include: a first transfer gear pair composedof a first input transfer gear on the first input shaft and a firstoutput transfer gear on the first countershaft; and a second transfergear pair composed of a second input transfer gear on the second inputshaft and a second output transfer gear on the second countershaft, andthe coupling devices may include: a first transfer coupling deviceselectively coupling the first transfer gear pair; and a second transfercoupling device selectively coupling the second transfer gear pair.

The first transfer coupling device may be disposed on the firstcountershaft and engaged with the first output transfer gear, and thesecond transfer coupling device may be disposed on the secondcountershaft and engaged with the second output transfer gear.

The shift gear pairs may include: a plurality of sub-shift gear pairshaving different gear ratios and disposed on the first countershaft andthe output shaft; and a plurality of main-shift gear pairs havingdifferent gear ratios and disposed on the second countershaft and theoutput shaft, and the sub-shift gear pairs and the main-shift gear pairsmay be configured such that shift gear pairs having the same gear ratiosexist.

The shift gear pairs may include: a plurality of sub-shift gear pairshaving different gear ratios and disposed on the first countershaft andthe output shaft; and a plurality of main-shift gear pairs havingdifferent gear ratios and disposed on the second countershaft and theoutput shaft, and the gear pairs may be configured such that a sameresultant gear ratio exists between resultant gear ratios of a gearratio of the first transfer gear pair and gear ratios of the sub-shiftgear pairs and resultant gear ratios of a gear ratio of the secondtransfer gear pair and the main-shift gear pairs.

The shift gear pairs having the same gear ratios may have gear ratiosover a specific gear ratio.

The sub-shift gear pairs and the main-shift gear pairs may share outputgears on the output shaft.

Torque transmitted to an output shaft from an engine in a specific rangeis smoothly changed by slip control of a clutch and relative rotationaction allowed by a one-way clutch in a process of shifting to a desiredrange, so deterioration of shifting ability, including a backwardpulling effect of a vehicle when shifting, is prevented.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the entire structure of atransmission for a vehicle according to an embodiment of the presentinvention.

FIGS. 2A to 2D are diagrams illustrating a process of shifting from anN-range to a 1-range by a transmission for a vehicle of the presentinvention.

FIGS. 3A to 3D are diagrams illustrating a process of shifting from the1-range to a 2-range by a transmission for a vehicle of the presentinvention.

FIG. 4 is a diagram illustrating the entire configuration of atransmission for a vehicle having another arrangement of a one-wayclutch according to an embodiment of the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

Exemplary embodiments of the present invention will be describedhereafter in detail with reference to the accompanying drawings.

A transmission for a vehicle according to an embodiment of the presentinvention may include a first input shaft INPUT1, a second input shaftINPUT2, a first countershaft CNT1, a second countershaft CNT2, coupling,coupling devices, a one-way clutch OWC, and a shifting mechanism 7.

Referring to FIG. 1, in detail, the first input shaft INPUT1 isconnected to a power source at a first end and can rotate bycontinuously receiving torque from the power source. The power sourcemay be an engine 1 and the first input shaft INPUT1 can continuously berotated by torque from the engine 1.

The second input shaft INPUT2 is connected to the power source through aclutch C at a first end and can rotate by selectively receiving torquefrom the power source in accordance with engagement and disengagement ofthe clutch C.

The first input shaft INPUT1 and the second input shaft INPUT2 may becoaxially arranged, in which the second input shaft INPUT2 may be ahollow shaft and the first input shaft INUPT1 may be inserted in thesecond input shaft INPUT2.

The first countershaft CNT1 may be connected with the first input shaftINPUT1 by a transfer gear pair.

For example, a first transfer gear pair 3 may be engaged with each otheron the first input shaft INPUT1 and the first countershaft CNT1,respectively, and may include a pair of a first input transfer gear 3Aon the first input shaft INPUT1 and a first output transfer gear 3B onthe first countershaft CNT1.

The first input transfer gear 3A cannot rotate relative to the firstinput shaft INPUT1 and the first output transfer gear 3B may rotaterelative to the first countershaft CNT1 or may be rotated relative tothe first countershaft CNT1 by the one-way clutch OWC, which will bedescribed below.

The second countershaft CNT2 may be connected with the second inputshaft INPUT2 by a transfer gear pair.

For example, a second transfer gear pair 5 may be engaged with eachother on the second input shaft INPUT2 and the second countershaft CNT2,respectively, and may include a pair of a second input transfer gear 5Aon the second input shaft INPUT2 and a second output transfer gear 5B onthe second countershaft CNT2.

The second input transfer gear 5A can rotate relative to the secondinput shaft INPUT2 and the second output transfer gear 5B can rotaterelative to the second countershaft CNT2.

The coupling device can transmit torque from the first input shaftINPUT1 to the first countershaft CNT1 and from the second input shaftINPUT1 to the second countershaft CNT2 by selecting the transfer gearpairs.

For example, the coupling device may include a first transfer couplingdevice ST1 selectively coupling the first transfer gear pair 3 and asecond transfer coupling device ST2 selectively coupling the secondtransfer gear pair 5.

That is, in shifting, by coupling the transfer gear pairs tocorresponding countershafts using the transfer coupling devices inadvance or after synchronization, torque from the power source can betransmitted from a shift gear pair making the current range to a shiftgear pair for making a desire range.

To this end, the first transfer coupling device ST1 may be disposed onthe first countershaft CNT1 and engaged with the first output transfergear 3B. Further, the second transfer coupling device ST2 may bedisposed on the second countershaft CNT2 and engaged with the secondoutput transfer gear 5B.

The first transfer coupling device ST1 may be disposed at a first sideor a second side of the first output transfer gear 3B and the secondtransfer coupling device ST2 may also be disposed at a first side or asecond side of the second output transfer gear 5B.

For example, the first transfer coupling device ST1 may be disposed at afirst side facing the engine 1 from the first output transfer gear 3B orat a second side facing the shifting mechanism 7 from the first outputtransfer gear 3B.

Further, the second transfer coupling device ST2 may be disposed at thesecond side facing the shifting mechanism 7 from the second outputtransfer gear 5B or at the first side facing the engine 1 from thesecond output transfer gear 5B.

All types of coupling devices for connecting/disconnecting power,including a synchro-mesh type synchronizer, a dog clutch, a modified dogclutch, a wet/dry clutch, an electric/electronic wet/dry magnet clutch,a coupling, a fluid coupling, and a spline, may be used as the firsttransfer coupling device ST1 and the second transfer coupling deviceST2.

The one-way clutch OWC is disposed on the first countershaft CNT1 andmay allow torque from the first input shaft INPUT1 to be transmittedonly to the first countershaft CNT1 from the first input shaft INPUT1and may prevent torque to be transmitted to the first input shaft INPUT1from the first countershaft CNT1.

For example, referring to FIG. 1, the one-way clutch OWC may be disposedin a power transmission path from the output transfer gear of thetransfer gear pair on the first countershaft CNT1.

For example, in a range gear (not given a reference numeral) that is thefirst output transfer gear 3B of the first transfer gear pair 3 and ashift gear (not given a reference numeral), the one-way clutch OWC maybe disposed at the middle of the range gear or between the range gearand the shift gear.

As another example, referring to FIG. 4, the one-way clutch OWC may bedisposed between the first countershaft CNT1 and the coupling devicethat selectively couples the output transfer gear of the transfer gearpair to the first countershaft CNT1.

For example, the one-way clutch OWC may be disposed between the firstcountershaft CNT1 and the first transfer coupling device ST1 couplingthe first output transfer gear 3B to the first countershaft CNT1.

That is, when the rotation speed of the first output transfer gear 3B islarger than the rotation speed of the first countershaft CNT1, the firstoutput transfer gear 3B forcibly rotates the first countershaft CNT1,but when the rotation speed of the first countershaft CNT1 is largerthan the rotation speed of the first output transfer gear 3B, relativerotation of the first output transfer gear 3B is allowed by the one-wayclutch OWC, so the difference in rotation speed between the firstcountershaft CNT1 and the first output transfer gear 3B can be absorbed.

The one-way clutch OWC may be used as a member mechanically connectingor disconnecting power, but a mechanical device operating in the sameprinciple, a hydraulic part or a hydraulic-mechanical composite device,or a device using electric/electromagnetic force may be used.

Next, referring to FIG. 1, the shifting mechanism 7 may include aplurality of shift gear pairs having different gear ratios on the firstcountershaft CNT1 and the output shaft OUTPUT, and the secondcountershaft CNT2 and the output shaft OUTPUT, and may change and outputpower from the power source, that is, the engine 1 to the output shaftOUTPUT by selecting a shift gear pair corresponding to the speed of avehicle using a synchronizer.

The output shaft OUTPUT, which is disposed in parallel with the firstcountershaft CNT1 and the second countershaft CNT2, may be arrangedcoaxially with the first input shaft INPUT1 and the second input shaftINPUT2. Further, though not shown in the figures, output transmitted tothe output shaft OUTPUT may be increased or decreased in speed throughanother pair of gears, a planetary gear set, or other transmissionelements and then transmitted to wheels.

Shift gear pairs of the shifting mechanism 7 may include sub-shift gearpairs and main-shift gear pairs. The sub-shift gear pairs may providedifferent gear ratios to the first countershaft CNT1 and the outputshaft OUTPUT and the main-shift gear pairs may provide different gearratios to the second countershaft CNT2 and the output shaft OUTPUT.

For example, the sub-shift gear pairs and the main-shift gear pairs mayinclude shift gear pairs having the same gear ratio.

The shift gear pairs having the same gear ratio may have gear ratiosover a specific gear ratio. As shown in FIG. 1, in the shift gear pairs,the gear ratios of the 1-range to the 5-rage sub-shift gear pairs GS1,GS2, GS3, GS4, and GS5 and the gear ratios of the 1-range range to the5-range main-shift gear pairs GM1, GM2, GM3, GM4, and GM5 may be madethe same.

That is, torque assist is more needed when shifting is performed with avehicle running at a relative low speed, so the sub-shift gear pairs andthe main-shift gear pairs for lower ranges may be given the same gearratios. Accordingly, it is possible to determine which ranges torqueassist is applied to in shifting on the basis of the ranges of thesub-shift gear pairs.

For example, in a 6-range transmission, when six ranges are made bymain-shift gear pairs and five ranges are made by sub-shift gear pairs,as shown in FIG. 1, torque assist can be achieved at all the ranges.

However, though not shown in the figures, when six ranges are made bymain-shift gear pairs and four ranges are made by sub-shift gear pairs,torque assist can be achieved in shifting only from the 1-range to the5-range.

Further, when six ranges are made by main-shift gear pairs and tworanges are made by sub-shift gear pairs, torque assist can be achievedin shifting only from the 1-range to the 3-range.

Further, in the present invention, the sub-shift gear pairs and themain-shift gear pairs may share the output gears on the output shaftOUTPUT.

For example, the 1-range, 2-range, 3-range, 4-range, and 5-rangesub-shift gear pairs GS1, GS2, GS3, GS4, and GS5 may be engaged witheach other on the first countershaft CNT1 and the output shaft OUTPUT,and the 1-range, 2-range, 3-range, 4-range, 5-range, and 6-rangemain-shift gear pairs GM1, GM2, GM3, GM4, GM5, and GM6 may be engagedwith each other on the second countershaft CNT2 and the output shaftOUTPUT. 1-range to 5-range sub-shift input gears on the firstcountershaft CNT1 and 1-range to 5-range main-shift input gears on thesecond countershaft CNT2 may form the sub-shift gear pairs GS1, GS2,GS3, GS4, and GS5 and the main-shift gear pairs GM1, GM2, GM3, GM4, andGM5 by sharing the output gears on the output shaft OUTPUT.

Synchronizers for selecting the sub-shift gear pairs and the main-shiftgear pairs may be disposed on the first countershaft CNT1 and the secondcountershaft CNT2, respectively.

For example, a sub-shift 1&2-range synchronizer SS1&2 may be disposedbetween sub-shift 1-range and 2-range input gears for sub-shifting, asub-shift 3&4-range synchronizer SS3&4 may be disposed between sub-shift3-range and 4-range input gears, and a sub-shift 5-range synchronizerSS5 may be disposed at a side of the sub-shift 5-range input gear.

Further, a main-shift 1&2-range synchronizer SM1&2 may be disposedbetween main-shift 1-range and 2-range input gears for main-shifting, amain-shift 3&4-range synchronizer SM3&4 may be disposed betweenmain-shift 3-range and 4-range input gears, and a main-shift 5&6-rangesynchronizer SM5&6 may be disposed between main-shift 5-range and6-range input gears.

In the present invention, the gear ratios of the sub-shift gear pairsand the main-shift gear pairs may be the same, but the gear ratios ofthe sub-shift gear pairs and the main-shift gear pairs may be differentand the resultant gear ratio transmitted to the output shaft OUTPUT fromthe sub-shift gear pairs and the resultant gear ratio transmitted to theoutput shaft OUTPUT from the main-shift gear pairs may be the same.

For example, the gear pairs may be configured such that the sameresultant gear ratio exists between the resultant gear ratios of thegear ratio of the first transfer gear pair 3 and the gear ratios of thesub-shift gear pairs and the resultant gear ratio of the gear ratio ofthe second transfer gear pair 5 and the gear ratios of the main-shiftgear pairs.

That is, the shift gear pairs may be configured such that the resultantgear ratio obtained by multiplying the gear ratio of the first transfergear pair 3 by the gear ratio of any one of the sub-shift gear pairs andthe resultant gear ratio obtained by multiplying the gear ratio of thesecond transfer gear pair 5 by the gear ratio of any one of themain-shift gear pairs are the same.

The operation and effect of the present invention are describedhereafter.

A process of shifting from the N-range (neutral) to the 1-range for alow speed is described with reference to FIGS. 2A to 2D.

The first input shaft INPUT1 is directly connected to the engine 1 whenthe vehicle is started, so the first input transfer gear pair 3 isrotated with the first input shaft INPUT1.

In this state, all the coupling devices in the transmission arepositioned for the neutral state, so load is not applied to theoperation of the engine 1 regardless of whether the clutch C is engagedor not.

When shifting to the 1-range is started, as shown in FIG. 2A, before theclutch C is engaged, the second output transfer gear 5B of the secondtransfer gear pair 5 is coupled to the second countershaft CNT2 by thesecond transfer coupling device ST2 and the main-shift 1-range inputgear is coupled to the second countershaft CNT2 by the main-shift 1&2synchronizer SM1&2.

In this state, as the clutch C is slowly engaged, as in FIG. 2B, thetorque from the engine 1 starts to be transmitted through the secondinput shaft INPUT2, so power is transmitted to the second countershaftCNT2 through the second transfer gear pair 5 and the vehicle can run inthe 1-range by the main-shift 1-range shift gear pair GM1.

Thereafter, as in FIG. 2C, the first output transfer gear 3B of thefirst transfer gear pair 3 is coupled to the first countershaft CNT1 bythe first transfer coupling device ST1 and the sub-shift 1-range inputgear is coupled to the first countershaft CNT1 by the sub-shift 1&2synchronizer SS1&2.

That is, when a vehicle runs in the 1-range, as in FIG. 2B, the firstinput shaft INPUT1 and the second input shaft INPUT2 rotate at the samerotation speed, in which the first transfer gear pair 3 and the secondtransfer gear pair 5 make the same gear ratio and the main-shift 1-rangeshift gear pair GM1 and the sub-shift 1-range shift gear pair GS1 alsomake the same gear ratio.

Accordingly, not only the first transfer gear pair 3 and the secondtransfer gear pair 5, but the main-shift 1-range shift gear pair GM1 andthe sub-shift 1-range shift gear pair GS1 are rotated with theirrotation speed synchronized, so the corresponding coupling device orsynchronizer can be safely coupled without coupling noise or damage ofthe first transfer gear pair 3 and the sub-shift 1-range shift gear pairGS1.

Next, as in FIG. 2D, the second transfer coupling device ST2 isdecoupled from the second transfer gear pair 5 and the main-shift 1&2synchronizer SM1&2 is decoupled from the main-shift 1-range shift gearpair GM1. However, the first input shaft INPUT1 remains directlyconnected to the engine 1, even though the second transfer gear pair 5and the main-shift 1-range shift gear pair GM1 are decoupled, so thetorque from the engine 1 keeps being transmitted to the output shaftOUTPUT through the first transfer gear pair 3, the first countershaftCNT1, and the sub-shift 1-range shift gear pair GS1, and accordingly,the vehicle can keep running forward in the 1-range.

Thereafter, torque transmitted from the engine 1 through the first inputshaft INPUT1 directly connected to the engine 1 keeps being transmittedto the output shaft OUTPUT through the first countershaft CNT1 even ifthe clutch C is disengaged, so the 1-range can be maintained.

Next, a process of shifting from the 1-range to the 2-range is describedwith reference to FIGS. FIGS. 3A to 3D.

When shifting from the 1-range to the 2-range is started, the secondoutput transfer gear 5B of the second transfer gear pair 5 is coupled tothe second countershaft CNT2 by the second transfer coupling device ST2with the clutch C disengaged, as in FIG. 3A.

In this state, as the clutch C is slowly engaged, as in FIG. 3B, thetorque from the engine 1 starts to be transmitted through the secondinput shaft INPUT2, so power is transmitted to the second countershaftCNT2 through the second transfer gear pair 5 and the vehicle can run inthe 2-range by the main-shift 2-range shift gear pair GM2.

In this case, before the clutch C is engaged, the first transfer gearpair 3 and the sub-shift 1-range shift gear pair GS1 are engaged and thevehicle runs in the 1-range, but after the clutch C is engaged, shiftingto the 2-range is made by the second transfer gear pair 5 and themain-shift 2-range shift gear pair GM2.

However, the difference in rotation speed between the first countershaftCNT1 and the first input shaft INPUT1, in which the first countershaftCNT1 rotates at a higher speed than the first input shaft INPUT1, due tothe difference in gear ratio between the sub-shift 1-range shift gearpair GS1 and the main-shift 2-range shift gear pair GM2 is allowed andabsorbed by the one-way clutch OWC, so the torque from the engine is nottransmitted from the first countershaft CNT1 to the first input shaftINPUT1.

Accordingly, in the process of shifting from the 1-range to the 2-range,the flow of power from the first countershaft CNT1 to the output shaftOUTPUT is smoothly changed to the output shaft OUTPUT from the secondcountershaft CNT2 by slip engagement control of the clutch C andrelative rotation allowed by the one-way clutch OWC, so deterioration ofshifting ability, including a backward pulling effect of a vehicle whenshifting, is prevented.

Thereafter, as in FIG. 3C, the first output transfer gear 3B of thefirst transfer gear pair 3 is coupled to the first countershaft CNT1 bythe first transfer coupling device ST1.

That is, when a vehicle runs in the 2-range, as in FIG. 3B, the firstinput shaft INPUT1 and the second input shaft INPUT2 rotate at the samerotation speed, in which the first transfer gear pair 3 and the secondtransfer gear pair 5 make the same gear ratio and the main-shift 2-rangeshift gear pair GM2 and the sub-shift 2-range shift gear pair GS2 alsomake the same gear ratio.

Accordingly, not only the first transfer gear pair 3 and the secondtransfer gear pair 5, but the main-shift 2-range shift gear pair GM2 andthe sub-shift 2-range shift gear pair GS2 are rotated with theirrotation speed synchronized, so the corresponding coupling device orsynchronizer can be safely coupled without coupling noise or damage ofthe first transfer gear pair 3 and the sub-shift 2-range shift gear pairGS2.

Next, as in FIG. 3D, the second transfer coupling device ST2 isdecoupled from the second transfer gear pair 5 and the main-shift 1&2synchronizer SM1&2 is decoupled from the main-shift 2-range shift gearpair GM2. However, the first input shaft INPUT1 remains directlyconnected to the engine 1, even though the second transfer gear pair 5and the main-shift 2-range shift gear pair GM2 are decoupled, so thetorque from the engine 1 keeps being transmitted to the output shaftOUTPUT through the first transfer gear pair 3, the first countershaftCNT1, and the sub-shift 2-range shift gear pair GS2, and accordingly,the vehicle can keep running forward in the 2-range.

Thereafter, torque transmitted from the engine 1 through the first inputshaft INPUT1 directly connected to the engine 1 keeps being transmittedto the output shaft OUTPUT through the first countershaft CNT1 even ifthe clutch C is disengaged, so the 2-range can be maintained.

Further, the other ranges can be achieved in the processes of shiftingdescribed above.

As described above, according to the present invention, torque from theengine 1 transmitted to the output shaft OUTPUT in a specific range issmoothly changed to the output shaft OUTPUT by slip engagement controlof the clutch and relative rotation action allowed by the one-way clutchOWC in a process of shifting to a desired range, so deterioration ofshifting ability, including a backward pulling effect of a vehicle whenshifting, is prevented.

Although an exemplary embodiment of the present invention has beendescribed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper”, “lower”, “inner” and “outer” are used todescribe features of the exemplary embodiments with reference to thepositions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A transmission for a vehicle, comprising: a firstinput shaft continuously receiving torque from a power source; a secondinput shaft selectively receiving torque from the power source through aclutch; a first countershaft and a second countershaft connected withthe first input shaft and the second input shaft, respectively, by atransfer gear pair; coupling devices transmitting torque to the firstcountershaft and the second countershaft from the first input shaft andthe second input shaft by selecting the transfer gear pairs; a one-wayclutch disposed on the first countershaft to allow torque provided tothe first input shaft to be transmitted only to the first countershaftfrom the first input shaft; and a shifting mechanism including aplurality of shift gear pairs having different gear ratios on the firstcountershaft, the second countershaft, and an output shaft, and changingand outputting power from the power source to the output shaft byselecting a shift gear pair corresponding to a speed of the vehicle,using a synchronizer.
 2. The transmission of claim 1, wherein theone-way clutch is disposed in a power transmission path from an outputtransfer gear of the transfer gear pair on the first countershaft. 3.The transmission of claim 1, wherein the one-way clutch is disposedbetween the first countershaft and one of the coupling devices, whereinthe one of the coupling devices selectively couples an output transfergear of the transfer gear pairs to the first countershaft.
 4. Thetransmission of claim 1, wherein the transfer gear pairs include: afirst transfer gear pair having a first input transfer gear on the firstinput shaft and a first output transfer gear on the first countershaft;and a second transfer gear pair having a second input transfer gear onthe second input shaft and a second output transfer gear on the secondcountershaft, and the coupling devices include: a first transfercoupling device selectively coupling the first transfer gear pair; and asecond transfer coupling device selectively coupling the second transfergear pair.
 5. The transmission of claim 4, wherein the first transfercoupling device is disposed on the first countershaft and engaged withthe first output transfer gear, and the second transfer coupling deviceis disposed on the second countershaft and engaged with the secondoutput transfer gear.
 6. The transmission of claim 1, wherein the shiftgear pairs include: a plurality of sub-shift gear pairs having differentgear ratios and disposed on the first countershaft and the output shaft;and a plurality of main-shift gear pairs having different gear ratiosand disposed on the second countershaft and the output shaft, whereinthe sub-shift gear pairs and the main-shift gear pairs are configuredsuch that shift gear pairs having a same gear ratios exist.
 7. Thetransmission of claim 3, wherein the shift gear pairs include: aplurality of sub-shift gear pairs having different gear ratios anddisposed on the first countershaft and the output shaft; and a pluralityof main-shift gear pairs having different gear ratios and disposed onthe second countershaft and the output shaft, wherein the gear pairs areconfigured such that a same resultant gear ratio exists betweenresultant gear ratios of a gear ratio of the first transfer gear pairand gear ratios of the sub-shift gear pairs and resultant gear ratios ofa gear ratio of the second transfer gear pair and the main-shift gearpairs.
 8. The transmission of claim 6, wherein the shift gear pairshaving a same gear ratios have gear ratios over a specific gear ratio.9. The transmission of claim 6, wherein the sub-shift gear pairs and themain-shift gear pairs share output gears on the output shaft.